Hello, Edward, & welcome. Thank you so much for starting your own topic. “me too” posts tend to really muddy the waters, as each configuration is diferent & it’s confusing when a reply to 1 person’s situation isn’t applicable to another person’s, even though it’s the same thread.
HTTP errors are indeed frustratingly vague. Unfortunately, there are quite a few causes to add to the vagueries involved. 1 of the most common, though, is improper configuration of 2 variables in the php.ini file, specifically, post_max_size & upload_max_filesize. The 2 should be = & be more than the size of the file you wish to upload.
If these are configured correctly, then other issues are likely afoot. Sometimes you can determine these either by looking at your site’s error logs via your hosting provider’s control panel, if that facility is available, or via error logs in your WordPress folder(s). Other causes of the problem can be firewall issues, either at the client’s or the server’s side, (or both), resource limitations, & even browser incompatibilities &/or misconfigurations.
It would really assist if you could be very specific regarding what you’re experiencing. Unfortunately, I’m afraid I don’t understand the part surrounded by *’s: “The person who normally does it reported the problem to me, and **I got the same — two different home networks.**”
